Now that Sunny had experienced moving up a class without simultaneously rising to a new Rank, he understood the difference between the two more clearly.
Ascending to a new Rank was a much more profound change. It elevated the quality of his shadow cores and essence, gifted him with new abilities, and allowed for a deeper access to his Aspect. The resulting jump in power was nothing short of tremendous.
Reaching a new Class, on the contrary, primarily affected the quantity of his shadow essence, and as such, the increase in power was much more gradual. Sunny didn't feel much stronger than he had a few hours ago… but that was because he had already been enjoying the extra strength and essence capacity for a long time.
